This invention relates generally to open-cell polyolefin foam with utility in both sound and thermal insulation applications and its preparation.
U.S. Pat. No. 5,348,795 discloses preparation of dimensionally stable, open-cell polypropylene foam products. Preferred propylene polymer resins are branched or lightly cross-linked. The examples that relate to extruded, coalesced foam strand structures have an open-cell content of 34-72 percent, a cell size of 0.36-0.85 millimeters (mm) and a density of 22.1-31.7 kilograms per cubic meter (kg/m3). It also discloses use of graphite forming plates that are lined with polytetrafluoroethylene sheet.
One aspect of the present invention is an extruded, open-cell, coalesced foam strand material that comprises a propylene polymer material and has a density of 22 kg/m3 or less (xe2x89xa6), preferably xe2x89xa620 kg/m3, an open-cell content of at least (xe2x89xa7) 50 percent and a cell size xe2x89xa6two mm.
In a related aspect, the material has an open-cell content xe2x89xa780 percent. The structure is preferably substantially free of mechanically induced perforation channels.
A second aspect of the invention is an extruded, open-cell, acoustically active, coalesced foam strand material that comprises a propylene polymer material and has a density of xe2x89xa6100 kg/m3, an open-cell content of xe2x89xa750%, a cell size of xe2x89xa6two mm and, in its extrusion direction, a noise reduction coefficient xe2x89xa70.3, the foam having defined therein a plurality of perforation channels, the channels being oriented in a direction generally perpendicular to the extrusion direction.
A third aspect of the invention is an extruded, open-cell, coalesced foam strand material that comprises a propylene polymer material and has a density xe2x89xa620 kg/m3 and an open-cell content xe2x89xa650 percent.
A fourth aspect of the invention is an extruded, substantially closed-cell, coalesced foam strand material that comprises a propylene polymer material and has a density of 20 kilograms per cubic meter or less, an open-cell content of less than 20 percent and a cell size of two millimeters or less.
A fifth aspect of the invention is a foam-forming apparatus comprising:
a) a foam extrudate receiving roller assembly;
b) a second roller assembly, the second roller assembly being connected to the foam extrudate receiving roller assembly by at least one articulated linkage; and
c) a foam tensioning assembly, the foam tensioning assembly being spaced apart from, but in operative relation to, the second roller assembly. In a related aspect, the apparatus further comprises a forming plate assembly. The forming plate assembly may either replace the second roller assembly or it may supplement roller assemblies a) and b). As a substitute, the forming plate assembly is preferably connected to the foam extrudate receiving roller assembly by at least one articulated linkage. As a supplement, the forming plate assembly is preferably connected in the same manner to the second roller assembly and spaced apart from, but in operative relation to the foam tensioning assembly. The forming plate assembly preferably has at least one lubricant applicator operatively connected thereto. The lubricant applicator preferably supplies a lubricant material to forming plate assembly surfaces that contact a foam material during operation of the apparatus.